This invention relates to a monitoring method and the system thereof for comparing the load current of a motor detected during operation with the load current thereof memorized during model operation and for watching out for overload of the motor.
Conventional systems such as the one shown in FIG. 1 have been proposed as monitoring apparatus. In the apparatus the load current LI of a motor is made to be applied to gates 2 and 3 through an AD converter 1, and when the apparatus is switched to model operation by a gate switch signal GC, a memory 4 is made to store the current value via the gate 2 and when the apparatus is operated at actual operation, the current value is input in a subtracter 5 via the gate 3. At the time of a normal operation, the subtracter 5 computes difference between the load current value of the model operation stored in the memory 4 and the current value at the actual operation transmitted from the gate 3 to obtain a subtraction value BV, a comparator 6 compares the subtraction value BV with a set value SV prescribed at a setter 7, and if the subtraction value BV is greater than the prescribed value SV, the comparator 6 outputs an alarm signal AL. The prior art apparatus, however, is defective in that the capacity of the memory 4 becomes enormous since load current values of the motor are AD-converted and all of those values are stored in the memory 4. That leads to such inconvenience as to require additional expensive exterior memory devices such as magnetic tapes.